You can check migration_dependencies in file yml. If the migration has dependencies. You must be migrate dependencies first.
– MrDSep 21 '18 at 3:48

so migration can be good with only running one or other group.Actually I use the default group only, except for files that is on error (I don't know why). But I do multiple tests.
– webmaster pfSep 21 '18 at 6:51

and what about the d7_ migrations ? needed or not, because I get errors on some.
– webmaster pfSep 21 '18 at 7:35